you won't be able to check whether your application is received through ECAS. Even though the system says you can use your receipt number to check your status, this is not the case. Only file numbers and UCIs are used to check your status, which may be received in the acknowledgement of receipt. If not, it will be on the Sponsorship Approval that is sent out.
At this point, you have quite a while to wait until you receive either one of those. It's been a trend AOR and SAs come within hours or days of eachother. Right now, they are processing applications received on March 21st. If you have tracking information for your package, it's suggested you check that to see if it's been received or signed for. You will not receive any notification that the package arrived.